Chemical agents, which is frequently referred to as collectors, are used in conjunction with froth flotation to aid the beneficiation or concentration of phosphate content, or P.sub.2 O.sub.5 from phosphate rock. Phosphate rock is a natural rock consisting largely of calcium phosphate and used chiefly as a raw material for manufacture of phosphate fertilizers, phosphate acid and phosphorous, and therefore indirectly used for practically all commercial phosphorus chemicals. In the U.S., most deposits of phosphate ores are located in Florida and North Carolina, especially in Florida, which produces 80% of United States and one third of the world phosphate rock. The deposit in Florida contains siliceous materials, such as silica which are valueless constituents. Other valueless constituents such as calcium carbonate, some carbonaceous materials and heavy metal minerals may also be contained in the deposit. In order to meet the chemical standard of phosphoric acid production, it is generally required to concentrate the phosphate content, generally measured by the "bone phosphate of lime" commonly abbreviated to BPL, by rejecting the valueless materials from raw phosphate minerals.
Many methods have been explored and used to beneficiate or concentrate the phosphate constituent by removing the siliceous, carbonaceous and other heavy metal constituents. Flotation is a principal means by which phosphate and other ores are concentrated. Generally, flotation is a process to separate finely ground valuable minerals from their associated gangue or waste, or to separate one valuable component from another. In froth flotation, frothing occurs by introducing air into a slurry of finely divided ore and water containing a frothing agent. Minerals that have a special affinity to air bubbles rise to the surface in the froth and thus are separated from the slurry. The particles to be separated by froth flotation must be of a size that can be readily levitated by the air bubbles. Generally, the size is below 16 mesh (-16 mesh or -991.mu.). In froth flotation, the raw minerals are classified into various fractions according to the size of the particle. In Florida phosphate industry, the raw minerals, which generally is called matrix, is classified into +16 mesh fraction, -16 to +150 mesh (+105.mu.) fraction, and -150 mesh fraction. The +16 mesh fraction, generally called pebble, is rich in BPL content and thus used directly for consumption at chemical plant. The -16 mesh to +150 mesh fraction is fed to beneficiation plant for flotation. The -150 mesh fraction, which primarily contains dry slime, is usually discarded as a waste prior to flotation.
Froth flotation agents used in conjunction with flotation must be capable of selectively coating the desired mineral material in spite of the presence of many other mineral species.
In a typical beneficiation process, the matrix is first sized to remove the pebble. Subsequently, the slime is removed in a hydro-cyclone from what constitutes flotation feed. The phosphate values are then extracted from the flotation sized slurry through a two-phase froth flotation process, frequently referred to as "Crago process" or "double flotation". This process consists of the following procedures: 1) conditioning the flotation feed materials with fatty acid and fuel oil, 2) flotation of the phosphate minerals in flotation cells, 3) deoiling with sulfuric acid to remove the reagents from the surface of the floated fraction, which is typically known as the rougher concentrate containing about 10% to 30% silica, 4) the rough concentrate go through another flotation with an cafionic reagent called amine being added and this time the silica is floated. The sink portion constitutes the final product called "the phosphate concentrate". The refloating, known as cleaner or reverse flotation, is needed to remove the remaining silica contained in the rougher concentrate and thus improve the grade of final concentrate phosphate.
A variety of promoters or additives for the anionic flotation of phosphate rock with fatty acids are know in the prior art. A promoter or an additive is a substance, which, when added to the flotation reagent, will significantly increase the recovery and/or grade of the phosphate material, thereby greatly increasing the efficiency and economics of the flotation process. Generally speaking, addition of surfactants or some other chemicals to the flotation reagents leads to a trade off between these two parameters: usually, an increase in recovery leads to a corresponding drop in selectivity or grade, and vice versa. In today's phosphate industry, recovery is most important and this invention has found a mixture of promoters or additives to increase both recovery and grade or increase recovery without decreasing the desired grade.
There are many United States patents which describe a combination of fatty acid and other surfactants for improved recovery or/and grade of phosphate or other non-sulfide ores by froth flotation. However, the results of these prior arts are not only limited to bench scale test, but also achieved recovery improvement without improving flotation economics.